Many electric drive vehicles, such as hybrid electric vehicles and electric cars, are propelled by motors when DC/DC converters boost DC power output by a low-voltage batteries, of about 200 V, and an inverter converts the thus-obtained high-voltage DC power into three-phase electric power, which is in turn used to drive the motors. The types of DC/DC converters frequently employed are ones that accumulate, in reactors, DC power supplied by low-voltage batteries, and employ switching elements, such as IGBTs, to switch accumulated electric power to raise voltages. Since the switching elements generate much heat, there has been proposed an example method according to which a base plate, to which switching elements are fixed, is mounted on a radiator, for which radiator fins are provided, so that heat generated by the switching elements is dissipated to cool the switching elements (see, for example, Patent Document 1).
In addition to switching elements that generate much heat, the DC/DC converter also requires power-generating elements, such as a coil, a transformer, and a capacitor, and a control element that controls the operation of the switching elements.
Since the use of switching elements is accompanied by the generation of much heat, generally, the switching elements are arranged on a cooler through which cooling water flows, and a control circuit board, on which a control element and power generating elements are mounted, is arranged above the cooler, at a distance from and parallel to a base plate, by means of a plurality of support columns that are provided on the cooler in order to reduce the size of the DC/DC converter (see, for example, Patent Document 2). In this arrangement, since the base plate and the control circuit board are arranged as two layers, above the cooler, the installation space can be reduced. Furthermore, with this arrangement, heat generated by the control circuit board can be transferred to the cooler via the plurality of support columns, and therefore, the switching elements and the individual power generating elements mounted on the control circuit board can be cooled. Moreover, according to Patent Document 1, previously described, the control circuit board is fixed to bosses, provided for the base plate, so as to arrange the switching elements and the control circuit board as two layers, and as a result, a saving in space is obtained.